Connector and Cable Choices for Gigabit Ethernet

Theneed for higher data communications speed is the driving force behind theevolution of Ethernet from 10MB/s up to 10GB/s bit rates. Currently, GBEthernet has four types of physical layer signaling: 1000Base-SX (shortwavelength optical fiber), 1000Base-LX (long wavelength fiber), 1000Base-CX(short run copper) and 1000Base-T (100m, four pair category 5 UTP).

Someapplications that need the kind of speed delivered by GB Ethernet include:

IndustrialAutomation Applications

On the industrial side, high-resolution videoapplications have been a leading force in seeking higher bit rates. This is dueto dense data content in high frame rate video, especially applicationsinvolving full color. This applies to both visible light and infrared (IR)cameras. In fact, full-color cameras with both visible light and IR imagingcapabilities are widely available, and can transmit images at full frame ratesof 400Hz and higher. These frames include not only images, but also temperaturemeasurements with 14-bit or higher resolution.

Mostindustrial video cameras used for machine vision automation and real-timeremote monitoring of critical equipment come with GB Ethernet Visioncapabilities. This includes the GB Ethernet Vision Control and StreamingProtocols (GVCP and GVSP, respectively). These capabilities allow an automatedapplication to detect and enumerate the cameras and define how they obtain avalid IP address. In addition, the application can configure cameras andreceive streaming data from them (bootstrap registers describe the cameras,including current IP address, serial number, manufacturer, etc.). Some of theseapplications take advantage of Power-over-Ethernet (PoE) to power the cameras.

Besidesmachine vision and other production automation systems, these capabilities areimportant in a variety of remote security, surveillance and monitoringapplications, which include: asset monitoring and protection (warehouses, bulkmaterial yards, etc.); process monitoring and control; machine conditionmonitoring; high-speed sorting; assembly verification and package inspection;and remote control of test and measurement systems.

Convergenceof Office IT and Automation

Besidesthe need for high data transmission speeds, another driving force behind theexpanding use of GB Ethernet (and Ethernet in general) is reduced capitalinvestment costs. Instead of having separate redundant networks, there is oneshared data communication system across IT and automation. But an automationenvironment has different cabling needs than an office IT environment. Thetypes of connectors and cables used in the office are not robust enough for thefactory floor. In order to successfully converge the two networks, passivecomponent requirements for both sides need to be taken into account.

Theideal solution is to use cables and connectors that meet the data speedrequirements of office IT networks, and provide the robustness, flexibility andease of assembly needed on the factory floor. This approach allows theresulting network to combine applications in a way that saves cost, increases speedand improves efficiencies. The resulting flexibility also allows the system tokeep up with changing automation needs and future data rate increases thatoffice IT staff will be keen to adopt.

Cableand Connector Selection

CAT5cables and connectors are fine at the lower Ethernet data rates. CAT6 hardwarebecomes a necessity for GB Ethernet. At GB Ethernet speeds, you can't view acable/connector interface as a lumped-element, but must treat it as atransmission line. More specifically, the effects of cable and connectorcapacitance can degrade the system's signal performance. Excess capacitiveloading can cause an impedance mismatch on the transmission line, signalreflections and distortion. Using cable and connectors that have minimalline-to-line and line-to-ground capacitance will help ensure an acceptableamount of signal distortion.

Forexample, Harting's line of RJ Industrial cables and connectors are suitable for10GB Ethernet, and have features that facilitate the convergence of office ITand factory automation systems. These designs evolved from the company's workon 4-pole CAT5 applications several years ago. Through the use of patented IDC(insulation displacement connector) technologies, the company's line of RJ45and M12 connectors allow for tool-less field assembly.

It'simportant to recognize that not all 8-wire cable is suitable for GB Ethernet.The jacket material, core structure, agency ratings, shielding, environmentalratings, etc. are all important considerations when selecting the correct cablefor the application. Many 8-wire Ethernet cables are only rated for CAT5applications, and may or may not have the ratings and specifications you need.

Theseconsiderations are particularly important when fabricating your own GB Ethernetcable assemblies. You don't want to invest in CAT6 connectors and put them onthe wrong cable. Therefore, selection of Ethernet cables and connectors shouldbe made at the same time to ensure compatibility. For example, if shieldedcable is required, then you need to make sure the shielding continues throughthe connector, i.e., the connector termination has to be compatible with thecable.

Steve Loyal is business development manager, deviceconnectivity solutions for Harting North America.